Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
Wireless service providers may operate access networks each arranged to provide wireless communication devices (WCDs), such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly-equipped communication devices, with wireless communication service. Each such access network may include a number of base stations that radiate to define an air interface over which to provide wireless service to WCDs according to an agreed air-interface protocol, such as Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Operability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1xRTT and 1xEV-DO), WIFI, and BLUETOOTH, or others now known or later developed. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a WCD within coverage of the access network may engage in air-interface communication with a base station and may thereby communicate via the base station with various remote network entities and/or with other WCDs served by the base station or by other base stations.
In accordance with an agreed air-interface protocol, the air interface provided by the access network may be comprised of various air-interface resources that are utilized by the base stations to serve WCDs. For instance, each base station may radiate to define one or more air-interface coverage areas, such as cells and cell sectors, in which WCDs can operate and engage in air-interface communication with the base station. Within each air-interface coverage area, the base station may operate on one or more carrier frequencies (or “carriers”), each defining a frequency channel for communicating with WCDs. In a typical example, the base station's one or more carriers may each take the form of a particular frequency block (e.g., a 1.25 MHz, 5 MHz, or 10 MHz block) in a profile frequency band used by the wireless service provider, such as a 800 MHz band, a 1.9 GHz band, or a 2.5 GHz band.
In practice, each of the base station's one or more frequency channels may be divided into a downlink (or forward link) for carrying communications from the base station to WCDs and an uplink (or reverse link) for carrying communications from WCDs to the base stations. For example, according to some air-interface protocols, each frequency channel may be divided over frequency into a first block of frequency for downlink communications and a second block of frequency for uplink communications. Alternatively, according to other air-interface protocols, each frequency channel may be divided over time into a first set of timeslots for carrying downlink communications and a second set of timeslots for carrying uplink communications. Other techniques for dividing a frequency channel into a downlink and uplink may exist as well.
Further, the agreed air-interface protocol may employ techniques such as time-division multiplexing, frequency-division multiplexing, and/or code-division multiplexing to further divide a frequency channel's downlink and/or uplink into discrete sub-resources (e.g., LTE resource blocks, 1xEV-DO forward-link timeslots and/or reverse-link channels, etc.), which may then be used to carry control and/or bearer data between the base station and WCDs on the frequency channel.
In operation, each base station may be configured to broadcast, on each of its one or more frequency channels, (1) a list of the frequency channel(s) provided by the base station and (2) a pilot (or reference) signal that WCDs are configured to monitor in order to evaluate coverage strength (e.g., signal strength and/or signal to noise ratio). For example, in a representative LTE system, each base station may broadcast, on each of its one or more frequency channels, a system information block (SIB) message that lists the frequency channels on which the base station provides service and a reference signal that LTE-compliant WCDs are arranged to monitor in order to evaluate LTE coverage provided by the base station. As another example, in a representative CDMA system, each base station may broadcast, on each of its one or more frequency channels, a Channel List Message (CLM) that lists the frequency channels on which the base station provides service and a pilot signal that CDMA-compliant WCDs are arranged to monitor in order to evaluate CDMA coverage provided by the base station. Other examples are possible as well.
When a WCD first enters into coverage of an access network, the WCD may then automatically scan the air interface in an effort to find the strongest available pilot signal, and the WCD may then register with the access network over the frequency channel associated with that pilot signal. For instance, the WCD may generally scan through various frequency channels and evaluate any pilot signals on those frequency channels in order to identify the frequency channel having the strongest pilot signal. In turn, the WCD may engage in registration signaling with the access network on that frequency channel in order to register with the access network. At some later time, the access network can then assign the WCD certain sub-resources on the frequency channel and begin exchanging bearer data with the WCD.